×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

transition starter from star to delta
3

transition starter from star to delta

transition starter from star to delta

(OP)
Hi everyone. I have a 132 kW motor with a star-delta starter. Full load amperage is 230A. I'm still confused about setting the timer relay. can you tell me how long it takes to switch the star connection to a delta motor to work safely? are there any standards regulate this issue?

RE: transition starter from star to delta

I have the following opinion for your consideration.
"..I'm still confused about setting the timer relay. can you tell me how long it takes to switch the star connection to a delta motor to work safely? are there any standards regulate this issue?"
1. The standard can not determine the time. It depends on the load. However there are standards regarding the trip time of the thermal over-load (e.g. Class 10, 20, 30).
2. Suggestion: Set the the time delay to say 20s. Start the motor and observe the current. Start timing when it starts from a higher value to gradually down to and maintaining at a lower value. If the time from start to the time it starts to lever off takes say 10s. Reset the time delay to 10s + 2s = 12s. After say half an hour, start the motor again, it should be able to perform the expected SD starting.
Che Kuan Yau (Singapore)

RE: transition starter from star to delta

Generally speaking, transition once line speed levels off and there is negligible further acceleration while in wye.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: transition starter from star to delta

Go with what che said.

I would have said you're looking about the 10 to 15 second mark, but many variables.

Just remember to un load the motor as much as possible otherwise it will not start.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: transition starter from star to delta

I am with cr on this one.
It depends on the application.
Star-delta start may be used to start medium or high inertia loads.
It may be used for very low inertia loads when the utikity demands reduced current starting for motors above a certain size or to linit voltage dip in a plant on a soft supply.
Too much variation to suggest any fixed time.
Do a test start and note the acceleration time.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: transition starter from star to delta

I would like to submit some additional information four your consideration.
1. It is correct to say that we expect the Speed to go up to say 75-80% during Star, before transfer to Delta. It is observed that the Speed is reflected on the Current. It is simple to observe the Current with a clamp-on meter or the ampere meter on the panel; than to take Speed measurement with a tachometer on the motor shaft.
2. It is preferred/suggested to connect L1 to U1 and V2; L2 to V1 and W2; L3 to W1 and U2 ; for CW rotation. There are other erroneous connections done for the past 75+ years, until being revised recently.
Che Kuan Yau (Singapore)

RE: transition starter from star to delta

Quote:

It is simple to observe the Current with a clamp-on meter or the ampere meter on the panel; than to take Speed measurement with a tachometer on the motor shaft.

True; but instead of complicating things by trying to use any kind of temporary tachometer, I'd simplify that and just listen to the sound of the machine, as you'll, unless hearing impaired, be able to discern when negligible further change is occurring. The result should be GE [good enough].

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: transition starter from star to delta

The difference between years of office theory and cr's years of experience actually doing it.
First choice. Sound
Second choice. Ammeter
Third choice. Tachometer? Overthinking it.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: transition starter from star to delta

4th choice: jettison the 19th century technology of Star-Delta starting and install a Solid State Soft Starter...

No transition time to determine, no transition spike of torque and voltage, no guessing on the settings of overloads and short circuit protection, no rapid deterioration of contactors from incorrect settings, no incorrect reconnection by inexperienced electricians, etc. etc. etc.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: transition starter from star to delta

"... I'd simplify just listen to the sound of the machine, as you'll, unless hearing impaired, be able to discern when negligible further change is occurring...".
1. True, but NOT always practical in the field. The machines is usually located some distance away from the the control station or the MCC, where the starting command is given; usually by push-button. Relating the sound to the speed is only possible at close proximity to the motor.
2. Observation of the current at the MCC starter panel amperemeter or with a clamp-on meter at the MCC instead of at the motor, is always practical.
Che Kuan Yau (Singapore)

RE: transition starter from star to delta

Quote (che12345)

True, but NOT always practical in the field. The machines is usually located some distance away from the the control station or the MCC, where the starting command is given...

A helper and pair of 2-way radios can often make it practical.

RE: transition starter from star to delta

Delta changeover can be done when the speed of the motor goes above 90% of its synch speed. By that time, the starting current is just tapering but not near no-load values. Best for you to do acceleration time estimates and set your changeover time from the results of what you get in your estimates.

RE: transition starter from star to delta

Quote (crshears)

Generally speaking, transition once line speed levels off and there is negligible further acceleration while in wye.
At that point, the current will also level off.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: transition starter from star to delta

"...No transition time to determine, no transition spike of torque and voltage, no guessing on the settings of overloads and short circuit protection, no rapid deterioration of contactors from incorrect settings, no incorrect reconnection by inexperienced electricians, etc. etc. etc".
I have the following opinion.
1. No transition time to determine. NOT true. It is necessary to set the Ramp-up time. Problem/damage may result for a 132kW, if the ramp-up time is erroneously set at say 5s or 30s.
2. No short circuit protection. NOT true. A proper breaker or high speed fuse per the manufacturer recommendation MUST be used in order to protect the SCR etc...
3. Soft starters are generally about 1.5 x the price of a SD assembly.
4. Most in-house technicians are NOT knowledgeable to repair a Soft starter.
5. A SD contactor assembly may last for 30+ years, double full for a Soft starter.
Summary: Soft starter has it advantages and disadvantages.
Che Kuan Yau (Singapore)

RE: transition starter from star to delta

Quote:

4th choice: jettison the 19th century technology of Star-Delta starting and install a Solid State Soft Starter...

No transition time to determine, no transition spike of torque and voltage, no guessing on the settings of overloads and short circuit protection, no rapid deterioration of contactors from incorrect settings, no incorrect reconnection by inexperienced electricians, etc. etc. etc.

Fair points, jraef, but many of these can be avoided and prevented without too much trouble, i.e. having electricians color code all wiring before disassembly so as to minimize the likelihood of incorrect reconnection.

Also, there are remote and not readily accessible locations where servicing of newer equipment can be problematic, and going with the simpler and field repairable without specialized expertise and/or customer support is worth considering.

RE: transition starter from star to delta

Current is the best way to set the transition time. Set to transition as the current drops to around FLA. Otherwise, go by acceleration sound.


Quote:

5. A SD contactor assembly may last for 30+ years, double full for a Soft starter.

We just had a customer asking if they should update their working soft-starters from 1994 last week.

RE: transition starter from star to delta

@ Mr LionelHutz
Thank you for your learned statement "Current is the best way to set the transition time. Set to transition as the current drops to around FLA. Otherwise, go by acceleration sound."
I would like to add the following.
For SD transition time
a) we are monitoring the Speed. Transfer when Speed is up to say >75%. The scientific/accurate measurement is by Tachometer, but cumbersome.
b) empirically it is observed that the Speed is reflected on the Current. As an alternative, Current measurement which is easily done instead of cumbersome Speed by tachometer.
c) Speed has NO relationship with the Sound level, which is dependent on the loudness and pitch. It is NOT acceptable scientifically to related the sound level to the speed, in this context . It is true to an experienced person would be able to "gauge" the speed based on the sound. It is unscientific.
Che Kuan Yau (Singapore)

RE: transition starter from star to delta

Quote:

a) we are monitoring the Speed.

No, that's not how reality works. I'd bet way less than 1% of wye-delta starter installations have ever monitored motor speed. Few monitor current. Most just go by the motor sound, or just guess at a time setting.

There is a difference in sound between a motor accelerating and a motor running steady state.

RE: transition starter from star to delta

Quote:

Speed has NO relationship with the Sound level, which is dependent on the loudness and pitch. It is NOT acceptable scientifically to related the sound level to the speed, in this context . It is true to an experienced person would be able to "gauge" the speed based on the sound. It is unscientific.

"Unscientific?" Really?

Respectfully, I submit that the working human ear, when teamed with a working human brain, is perfectly capable of detecting whether there is any discernible delta f over time.

If this were not so, music would have to be declared both unscientific and non-mathematical.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: transition starter from star to delta

Quote:

Transfer when Speed is up to say >75%.

This is wrong too, Transferring at 75% speed would draw high enough currents and cause such a surge that it's hardly worth using the wye-delta starter. The current at 75% speed is typically 75-90% of LRA so transitioning at such a low speed will cause most of the same inrush current and it's associated effects on the power system as just starting across the line would.

You want to transfer in the 90-95% speed range when the current has dropped close to or below FLA.

RE: transition starter from star to delta

Transfer at the greatest possible speed. That is when acceleration stops.
Detectable by ear or by current monitoring.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: transition starter from star to delta

@waross,
That's a better way of saying it.
But, like manually synchronizing a generator unit, you would turn the CB switch knob just when you see the synchro hand nears the 12 o' clock position, not after.

RE: transition starter from star to delta

Quote:

But, like manually synchronizing a generator unit, you would turn the CB switch knob just when you see the synchro hand nears the 12 o' clock position, not after.

???

Motor type hasn't been specified in OP, but I neither thought of nor saw any use of a synchroscope in SD motor starting.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: transition starter from star to delta

@cr,
Please take note of the use of the word "like". That means, it is not the thing, it is just "like" in plain English.

RE: transition starter from star to delta

Gotcha.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: transition starter from star to delta

The consequence of a late closing of a generator breaker are much more severe.
It may result in mechanical damage and currents in excess of normal fault currents.

Late transition of a star-delta starter results in some extra heating which may be acceptable, especially for a single start.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: transition starter from star to delta

We did have lots of damaged contactors that were traced to wrong setup of transition timing. The worst situation was when the arc chutes themselves helped in the destruction, the chutes accumulated previous debris, the contact arc sustained when switching happened.

RE: transition starter from star to delta

If the gear is setup so that the delta configuration leads the wye configuration rather than lagging it, the performance will be affected. Mechanicalshock and electrical transients.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: transition starter from star to delta

@ Mr Parchie (Electrical)7 Jun 24 03:15
"..We did have lots of damaged contactors that were traced to wrong setup of transition timing..."
Please advise what is/are the root/main cause. Following are some example.
a) transition time is based on Current?
b) transition time is base on Sound?
c) transition time is too short, while the motor is speeding up say around 50-60% rated speed, while the current is still at high level.
d) transition time is too long, after reaching say 90% rated speed, while the current has gone down?
e) transition time is too short, motor speed remains at say 50-60% rated speed; while the current remains at high level? [This is the case that the motor is undersize]
f) start/delta transition timer reset time is too short (<50ms) that causes short circuit on the contactor during transition?
g) no mechanical inter-lock between the Star and the Delta contactor?
h) others...
2. Please advise how to set the transition time.
Che Kuan Yau (Singapore)

RE: transition starter from star to delta

"...If the gear is setup so that the delta configuration leads the wye configuration rather than lagging it, the performance will be affected. Mechanicalshock and electrical transients".
I have the following opinion.
1. The gear/contactors set up does NOT determines the delta configuration leads the wye configuration rather than lagging it.... It is the wiring connection from the starter to the motor windings.
2. In Europe/IEC world, LV motors having 6 wires terminated on terminal block, where connection in Star, Delta or Star/Delta is possible at the field.
2.1 In US world, NEMA motors usually having 3 leads, where start/delta configuration at the field is IMPOSSIBLE. There are other formations on the market.
3. In Europe/IEC world, all major starter manufacturers had revised their wiring connection some 25+ years ago, after proven that the erroneous "standard" SD connection for the past 100+ years !. This is NOT so in the US world.
4. The revised Delta connection for CW rotation per IEC is L1-U1-V2; L2-V1-W2; L3-W1-U2 . There are other possible connections.
Che Kuan Yau (Singapore)

RE: transition starter from star to delta

@che,
The only way you can be sure the motor is very near it's rated speed is to do a motor acceleration time simulation. There are softwares that offer to do those. But you can calculate yourself using the well-extablished motor equations.

RE: transition starter from star to delta

@ Parchie (Electrical)9 Jun 24 22:25
"..The only way you can be sure the motor is very near it's rated speed is to do a motor acceleration time simulation. There are softwares that offer to do those. But you can calculate yourself using the well-extablished motor equations".
I have the following opinion.
1. Use a tachometer take measurement on the motor shaft. It cost very little but achieve very high accuracy.
2. Computer software produce "theoretical values" (not the actual running value at the field). The software and correct data needed to set up is usually cost prohibitive. Unless you are a big timer, regularly involved in commissioning big motors, or where cost is of no consideration.
Che Kuan Yau (Singapore)

RE: transition starter from star to delta

I have to wonder how many of our posters have actually started a large motor.
The old compensators we used to use for high inertia motors depended on the the operator going by the sound of the motor to make the manual transition from auto-transformer to DOL.
They did have a current operated safety solenoid.
On the side of the compensator was an iron handle about three feet long.
To start the motor the handle was quickly and firmly pulled back.
That started the motor on the auto-transformer.
When the motor had accelerated enough, the handle was rapidly pushed forward (actually, slammed forward) to change the connections from auto-transformer to DOL.
If the current had not dropped enough the blocking solenoid stopped the travel half way.
That would jar your arm up to your shoulder.
The operators quickly learned to properly judge the proper speed for transition.
Why did we slam the handle back and forth?
The copper contacts were operated directly by the action of the handle mechanism.
The faster the motion the less arcing.
Eventually, an electrician would spend most of a Sunday shift stripping down the compensator and filling the copper contacts to remove the pitting and arc craters.
After a couple of rebuilds, they contact set would be completely replaced.
The faster you slammed the handle, the longer you could go between rebuilds.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: transition starter from star to delta

Quote:

But you can calculate yourself using the well-extablished motor equations.

The equations I've seen are rather poor and not accurate.

RE: transition starter from star to delta

@ Mr Parchie (Electrical)9 Jun 24 22:25
1. I am still looking forward to your learned advice on the questions I had raised on 7th instant, on your long bad experience "We did have lots of damaged contactors that were traced to wrong setup of transition timing...".
2. Your kind learned experiences on the root cause would certainly be appreciated and be beneficial to all the readers.
Che Kuan Yau (Singapore)

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close